It’s summer. Hugo, a nine-year-old boy, is going to spend the summer in the seaside house where his father grew up. Grandma Sara wanted to gather the whole family for her birthday. One evening, she tells them that a wolf will come to take her away on her 80th birthday, as promised long ago. For the adults, it’s just an old legend made up by Grandma Sara, but for the children, a great and mysterious adventure is about to begin.